1. Field of the Invention
The present invention relates to a fixing element, and more particularly, to a fixing element for rotatably fixing a ribbon roller in a ribbon cartridge.
2. Description of the Prior Art
Ribbons of thermal printers are typically rolled on two ribbon rollers, which are respectively positioned on each side of a ribbon cartridge. However, there is no fixing mechanism available for firmly fixing the ribbon rollers within the ribbon cartridge. This results in undesirable rotation of the ribbon roller due to external vibration or shock when transporting the ribbon cartridge, which can cause the ribbon to become wrinkled. Printing quality can be detrimentally affected if the ribbon is wrinkled.
Generally, the prior art prevents the ribbon roller from rotating via a friction force. Please refer to FIG. 1, which is a diagram of preventing a ribbon roller 12 from rotating according to the prior art. There is a block 14 positioned at an end of a ribbon-feeding bay in a ribbon cartridge 10. The length of the ribbon roller 12 is longer than a distance between the block 14 and a base 16, so that the ribbon roller 12 presses the block 14. The pressed block 14 can provide a restoring force to the ribbon roller 12 towards the base 16, resulting in generation of a friction force between the ribbon roller 12 and the base 16 that prevents the ribbon roller 12 from rotating. Additionally, the block 14 can be replaced by other flexible elements, which can provide a force to push the ribbon roller 12 towards the base 16.
However, the block 14 is formed along with the ribbon cartridge 10. When manufacturing the ribbon cartridge 10, the distance between the block 14 and the base 16 has some tolerance, causing the restoring force to be inconsistent and thus the friction force to vary. If the friction force is too small, the ribbon might end up dangling out of the ribbon cartridge 10. On the contrary, if the friction force is too large, a printer cannot make the ribbon rotate. Additionally, if the block 14 is replaced by a spring or a flexible element, the restoring force may vary due to elastic fatigue.
Please refer to FIG. 2, which shows an etched surface 17 engaging a protrusion 18 to prevent the ribbon roller 12 from rotating based on the prior art. In order to control the friction force, the etched surface 17 is placed at the end of the ribbon roller 12 contacting the base 16, and the protrusion 18 is placed at the base 16 to engage the etched surface 17 so as to prevent the ribbon roller 12 from rotating. However, this method cannot absolutely solve the problem. If the restoration force provided by the block 14 is not large enough to make the etched surface 17 engage the protrusion 18, the ribbon roller 12 might rotate.